A conventional collapsible holder for drinking vessels shown in FIGS. 1 comprises a vertical position plate 10, a holding plate 11 pivotally connected with an upper inner side of the position plate 10 and a plate cap 12 pivotally connected with a lower inner side of the position plate 10 and two plate springs 13, 14 with an upper sloped portion and a lower sloped portion fixed vertically spaced apart in parallel on an inner surface of the position plate. Then the holding plate 11 and the plate cap 12 are collapsed relative to the position plate 10 to become flat or to be swung open for 90.degree. to each other for holding a drinking vessel put through down the hole in the holding plate 11 to sit on an inner surface of the plate cap 12. But the size of the hole for a drinking vessel is constant, not adjustable, and inconvenient.